I have been making and selling silicone gloves for many years now and in your instance of,

"My glove seems to be somewhat unflexible, when the silicone was setting I left it on my hand (which which in a stick holding position) for about 1 and a half hours, so it is roughly in position, but it seems quite tight round the fingers when it is fully griping the stick. Does anyone have an idea why this is happening?"

Then answer is very simple. The silicone is contracting as it cures and also because your hand was in the "stick holding position". However, if you were to simply hold your hand in a closed fist position as the silicone cures, the shape of your fingers will be more than what you need for the stick holding position. Therefore, you can essentially open up your hand slightly to grip the stick and it won't feel tight anymore.